Chang-Ming Cheng (National Taiwan Normal University)
In star formation, the first hydrostatic core is the first stable object before protostar formation. It is opaque to thermal radiation. Thus, the contraction is adiabatic at this stage and the temperature in the first core increases until molecular hydrogen dissociation begins at 2000 K. The sublimation temperature of calcium–aluminium-rich inclusion, around 1500 K, is the highest sublimation temperature among the solid matter in the solar system. Many people consider that calcium–aluminium-rich inclusion formed by cooling in the protoplanetary disk. However, before the stage of protoplanetary disk formation, the temperature in first hydrostatic core can reach above 1500 K. If there are some mechanisms to transport matter outwards, the cooling will lead to formation of calcium–aluminium-rich inclusion in outer region at this stage. Convection and diffusion are possible mechanisms to transport matter outwards but our calculation showed that the first hydrostatic core is stable against convection. Thus, diffusion is the only possible mechanism. We postulate that the accretion process at this stage results in internal gravity waves which are caused by density gradient and we expect that these waves drive diffusion. In order to describe diffusion, we want to calculate the diffusion coefficient by relating to the wave amplitude. Our goal is to build a model to describe the diffusion process within the first hydrostatic core.